commands: use bookmarks.validdest instead of duplicating logic Now that bookmarks.py has grown a validdest method that even handles successor changesets, we use that instead of duplicating the logic in commands.py

update: consider successor changesets when moving active bookmark Previously, when an obsolete changeset was bookmarked, successor changesets were not considered when moving the bookmark forward. Now that a bare update will move to the tip most of the successor changesets, we also update the bookmark logic to allow the bookmark to move with this update. Tests have been updated and keep issue4015 covered as well.

merge: consider successor changesets for a bare update Previously, a bare update would ignore any successor changesets thus potentially leaving you on an obsolete head. This happens commonly when there is an old bookmark that hasn't been moved forward which is the motivating reason for this patch series. Now, we will check for successor changesets if two conditions hold: 1) we are doing a bare update 2) *and* we are currently on an obsolete head. If we are in this situation, then we calculate the branchtip of the successor set and update to that changeset. Tests coverage has been added.

merge: refactor initialization of variables in update There is no code change here but this helps prepare for future commits that will fix a bare update with obsolete markers.

merge: update comment for future devs

obsolete: clarify documentation for succcessorssets

backout: add a message after backout that need manual commit In some case Backout silently succeeded to back out but left all the change uncommitted. This may be confusing for user so this changeset add a note reminding to commit. Other backout case already actively informs the user about created commit.